Mixing ingredients where portion of one of ingredients is a fn of the final amount

I have two mixtures of flour and water.

Mixture 1 has equal parts flour and water

Mixture 2 has two parts flour to one part water

I also have supplies of flour and water

Problem (a) I'm going to mix flour and water and want to end up with mixture 1 -- equal parts flour and water. BUT in doing so I have to include an amount of Mixture 2 that is 1/6 of the total amount of mixture I end up with (i.e., 1/6 of the total of flour, water, and mixture 2).

Problem (b) is similar -- I'm going to mix flour and water and want to end up with mixture 2 -- two to one ratio of flour to water. BUT I have to include an amount of Mixture 1 that is 1/7 of the total end result.